The present invention relates to a sliding mode controlling apparatus and a sliding mode controlling method for controlling the behavior of an elastic system, such as a spring-mass system.
For example, Japanese Laid-Open Patent Publication No. 9-217859 discloses a control system having a spring-mass system such as an electromagnetic valve. In such a control system, the state quantity, which includes, for example, the moved amount and the moving speed of a controlled subject, is feedback controlled through, for example, Proportional, Integral, Derivative (PID) control, such that the state quantity follows a target state quantity. However, the robustness of the prior art controlling methods, such as PID control, cannot be reliably maintained against disturbances and changes in characteristics of the controlled subject.
Accordingly, sliding mode control has been applied to such control systems. In the sliding mode control, the state quantity of a controlled subject converges on a switching hyperplane represented by a favorably designed linear function. Also, the state quantity is prevented from leaving the switching hyperplane.
Therefore, the sliding mode control guarantees a sufficient robustness against disturbances and changes in characteristics of the controlled subject and also prevents the state quantity of the controlled subject from leaving the switching hyperplane.
When the control performance of the sliding mode control is determined for controlling a subject, a switching hyperplane needs to designed to match several requirements. In this case, the requirements can contradict one another.
For example, in the control of the electromagnetic valve disclosed in the above publication, not only a stable operation, but also reduction of power consumption and prevention of noise produced by the action of the valve body are important factors that must be taken into consideration when determining the performance of the valve. If the sliding mode control is applied to the prevention of noise produced by opening and closing of the valve body, the switching hyperplane will be typically designed as follows. That is, the switching hyperplane is designed such that, when the valve body, which is the controlled subject, is moved from a first end of movement to a second end of movement, the moving speed of the valve body is decreased immediately before the valve body reaches the second end of movement. However, such design of the switching hyperplane will extend the time required for the valve body to move from the first movement end to the second movement end.
In this manner, when the switching hyperplane of sliding mode control is designed, several factors are often considered for improving the control performance. However, the required factors also often contradict one another. The contradictions of the required factors significantly hinder improvement of the control performance.
Accordingly, it is an objective of the present invention to provide a sliding mode controlling apparatus and a sliding mode controlling method that satisfy two or more requirements without contradiction when controlling the behavior of an elastic system such as spring mass system.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a sliding mode controlling apparatus for a controlled subject urged by an elastic member is provided. The controlled subject is movable between two movement ends. When the controlled subject is moved from a first movement end, which is one of the movement ends, to a second movement end, which is the other one of the movement ends, the controlling apparatus controls the controlled subject such that the state quantity of the controlled subject converges on a previously set switching hyperplane. The controlling apparatus includes changing means, which changes the switching hyperplane in accordance with the position of the controlled subject.
The present invention may also be applied to a sliding mode control method for a controlled subject urged by an elastic member. The controlled subject is movable between two movement ends. The method includes: controlling the controlled subject such that the state quantity of the controlled subject converges on a previously set switching hyper plane when the controlled subject is moved from a first movement end, which is one of the movement ends, to a second movement end, which is the other one of the movement ends; and changing the switching hyperplane in accordance with the position of the controlled subject.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.